Hip joint endoprostheses are implanted in large numbers worldwide. Unfortunately, in a small percentage of cases, hip joint endoprostheses are colonized by microbial microorganisms, particularly Gram-positive bacteria and also Gram-negative bacteria, and to a very small extent by yeasts and fungi. These microbial microorganisms, mainly typical skin microbes such as Staphylococcus aureus and Staphylococcus epidermidis, may enter a patient's body during a surgical operation (OP). It is also possible for microbial microorganisms to enter hip joint endoprostheses hematogenically. Where hip joint endoprostheses are colonized by microbial microorganisms, the surrounding bone and soft tissue also become infected and damaged by the microbial microorganisms.
The prior art primarily encompasses two treatment methods for infected hip joint endoprostheses, one-stage septic revision and two-stage septic revision. There are also a number of further treatment methods, such as for example the application of suction/irrigation drains.
In the case of one-stage revision, within one OP first of all the infected hip joint endoprosthesis is removed, next radical debridement is performed and then a revision hip joint endoprosthesis is implanted.
In two-stage septic revisions, in a first OP the infected hip joint endoprosthesis is initially removed, then debridement is performed and thereafter a hip joint spacer is implanted. The hip joint spacer consists of a stem, a collar, a neck and a ball head and replicates hip joint endoprostheses in shape and size. The hip joint spacer is anchored to the proximal femur with bone cement. The hip joint spacer remains for up to several weeks in the patient until the inflammation has subsided and the clinical inflammation markers have receded. The hip joint spacer is then removed in a second OP and a revision hip joint endoprosthesis implanted after fresh debridement.
US 2010/0042213 A1 discloses a hip joint prosthesis with a reservoir for liquid inside the implant. A hip spacer is known from WO 2017/178951 A1 which has recesses, wherein a substance for treating the bone may be introduced into the recesses. U.S. Pat. No. 6,245,111 B1 proposes a hip joint prosthesis, the surfaces of which are coated with an antibiotic. U.S. Pat. No. 5,681,289 B1 discloses a device for distributing a liquid active ingredient with the assistance of a bladder inside the device.
It is known to use spacers provided with antibiotics. Hip joint spacers may on the one hand be produced by the OP personnel during the OP itself from PMMA bone cement powder, antibiotics and monomer liquid, for example with a spacer shape, as described for example in patents DE 10 2015 104 704 B4 or EP 2 617 393 B1; on the other hand it is also conventional to use hip joint spacers prefabricated industrially from bone cement.
In spacers to date, antibiotics have been added to the cement powder before actual spacer production. Spacers are then cast using this antibiotically modified bone cement powder and subsequently harden by polymerization with the assistance of a monomer liquid added to the cement powder. The bone cement paste thus substantially encloses the antibiotics. Only the antibiotic particles situated in areas close to the surface are released under the action of bodily fluids, such as wound secretions. Active ingredient release is greatest at the start and then diminishes over the course of several days. Thereafter, only small quantities of the antibiotics continue to be released. The majority of the added antibiotics remains in the hardened bone cement of the spacers. In the case of spacers hitherto manufactured from bone cement, a subsequent change in the type and number of antibiotics used is not possible after spacer production or after implantation. It is moreover likewise impossible to adjust a defined concentration of antimicrobially active ingredients in the wound secretions or the bodily fluid surrounding the spacer.
In patent EP 1 991 170 B1 a hip joint spacer is described in which the ball head and the stem may be assembled by the user, wherein the ball head contains a first active ingredient and the stem is provided with a second active ingredient.
A further hip joint spacer is disclosed in US 2011/0015754 A1. In this spacer system, two cylindrical cavities are provided in the ball head which emerge with a narrow side at the ball surface. The two cavities are each closed with a liquid-permeable cap. Both cavities may be filled with antibiotic solutions. After implantation, the antibiotic solutions migrate through the liquid-permeable caps to the surface of the spacer.
In the case of two-stage septic revision, drains are also used during implantation of the hip joint spacers, these being intended to carry away wound secretions, blood and debris. The drains remain inside the patient for up to several days. The antibiotic active ingredients released by the spacer are taken up by the wound secretions and carried out via the drain. This means that a proportion of the antimicrobial active ingredients for protecting the spacer surface from microbial colonization are lost.